Many medical etiologies can be monitored periodically by analysis of a sample of a body fluid for the presence and level of a specific solute or component in the fluid. The most widely known example is the measurement of glucose levels in blood or interstitial fluid, pertaining to monitoring, treatment and control of diabetes mellitus.
Prior art blood glucose measurement devices have operated on the principle of taking blood from an individual by a variety of methods, such as by needle or lance, followed by contacting a diagnostic strip with a portion of the blood sample. Some recent devices appear to extract a sample of interstitial fluid rather than blood for purposes of the same type of analyses. The diagnostic test strip typically consists of a paper or microporous polymeric film which has been impregnated with a set of chemicals that, upon contact with the fluid, produce a measurable chemical reaction consistent with both the presence and concentration of a targeted analyte in the fluid. Most such test strips produce a color change, the spectral band and intensity of which are measured photometrically and correlated with analyte concentration. Numerous blood glucose meters are on the market which measure the level of blood glucose by color changes on test strips. Competition between manufacturers of these devices includes, in addition to cost, claims for accuracy, precision, small sample size, and, very importantly, speed of analysis. The latter-most factor becomes very important to a patient when all the other factors are balanced out.
One of the prior art devices presently in commercial use is a monitor/combination incorporating features disclosed and described in U.S. Pat. No. 4,787,398, wherein a hand-held, pocketable, diagnostic monitoring system contains a lancet unit and a means for accepting and reading a disposable diagnostic test strip upon which a droplet of blood is deposited. The disposable test strip contains a reagent package including glucose oxidase and a color-producing substrate, and a wicking means to distribute fluid from a blood droplet to the reagent package, which itself is immobilized on a porous medium addressable by a light source and a light sensing means. The wicking means is commonly a woven cotton-containing fabric, chosen because of the wettability and wicking nature of cotton fibers. Such fabrics are typically a blend of cotton and polyester. Such fabrics achieve a wicking delivery of a fluid such as blood to the reagent package, but not without drawbacks. One key factor is the relatively slow speed of wicking associated with this fabric. Another key factor is the characteristic of the cotton to absorb a portion of the fluid, such that the amount available to be delivered to the reagent package is significantly diminished. As a result, a greater amount a fluid, such as the blood droplet size, is required for analysis, and inadequate sample size or delivery often results in no reading or improper reading in a blood glucose monitor.
One significant aspect and feature of the present invention is a diagnostic test strip with an improved wicking material that provides a far greater rate of fluid transfer than presently available, so as to reduce the time necessary for sample fluid delivery to an immobilized reagent package, and thereby improve the speed of analysis.
Another significant aspect and feature of the present invention is a diagnostic test strip with an improved wicking material that provides a more even delivery of sample fluid to an immobilized reagent package, so as thereby to improve the precision and accuracy of analysis.
A further significant aspect and feature of the present invention is a diagnostic test strip that delivers a sample fluid to immobilized reagent package with such reliability, that a greater overall number of test strips meet manufacturing standards, resulting in little or no rejects and thereby lower overall manufacturing costs, ultimately resulting in lower overall cost to the patient.
These and other objects and attendant advantages of the present invention will be readily appreciated and understood by reference to the following summary of the invention and detailed description, considered in connection with the accompanying drawings.